Many nonwoven commercial products are formed from spunlaid fibers of polymeric resins. For instance, spunlaid fibers may be used to make diapers, feminine hygiene products, adult incontinence products, packaging materials, wipes, towels, dust mops, industrial garments, medical drapes, medical gowns, foot covers, sterilization wraps, table cloths, paint brushes, napkins, trash bags, various personal care articles, ground cover, and filtration media.
Spunlaid fibers are generally made by a continuous process, in which the fibers are spun and dispersed in a nonwoven web. Two examples of spunlaid processes are spunbonding or meltblowing. In particular, spunbonded fibers may be produced by spinning a polymeric resin into the shape of a fiber, for example, by heating the resin at least to its softening temperature, extruding the resin through a spinerette to form fibers, and transferring the fibers to a fiber draw unit to be collected in the form of spunlaid webs. Meltblown fibers may be produced by extruding the resin and attenuating the streams of resin by hot air to form fibers with a fine diameter and collecting the fibers to form spunlaid webs.
The textile industry consumes a large amount of thermoplastic polymeric resin each year for the production of nonwoven products. While it is known to incorporate various mineral fillers such as calcium carbonate and kaolin during production of nonwoven products and plastic products such as films and molded parts, it is not general practice to include large amounts of such fillers in polymeric nonwoven fibers. Previously, the cost of virgin resin was lower than the cost of concentrates composed of resins and mineral fillers and, thus, there was not a recognized need to incorporate significant amounts of such fillers into nonwoven products. However, due to recent increases in resin prices, there is now a cost benefit associated with increasing the quantity of mineral fillers and decreasing the quantity of resin in nonwoven products. By incorporating an optimum amount of at least one mineral filler, such as coated calcium carbonate, it is possible to reduce the required amount of virgin resin material while still producing a nonwoven product having comparable quality in terms of fiber strength, texture, and/or appearance.
The prior art appears to disclose nonwoven products comprising various amounts of inorganic compounds and/or mineral fillers. For example, U.S. Pat. No. 6,797,377 appears to disclose nonwoven webs comprising from 0.1 to 10 wt % of at least one mineral filler such as calcium carbonate, but imposes the limitation of the filler being used in conjunction with titanium dioxide in a mixture of at least two resin polymers. U.S. Pat. No. 6,759,357 likewise appears to disclose nonwoven fabrics comprising from 0.0015 to 0.09 wt % of at least one inorganic compound. S. Nago and Y. Mizutani, “Microporous Polypropylene Fibers Containing CaCO3 Filler,” 62 J. Appl. Polymer Sci. 81-86 (1996), also appears to discuss polypropylene-based nonwoven fibers comprising 25 wt % calcium carbonate. WO 97/30199 may disclose fibers consisting essentially of 0.01 to 20 wt % inorganic particles, substantially all having a Mohs hardness of less than about 5 and at least 90 wt % of the inorganic particles having a particle size of less than 10 microns. However, those references do not appear to disclose reducing the impact of the filler on the properties of the nonwoven fibers at least through changes to the particle size of the coated calcium carbonate by its average particle size and/or by its top cut.
Thus, it would be useful to provide spunlaid fibers that incorporate higher levels of coated calcium carbonate, thereby allowing for more cost-effective nonwoven products that have comparable quality in terms of strength, texture, and/or appearance.